Conventional plied yarns are made of either staple or filament yarns. In making a plied yarn from staple yarn, the staple yarn must be processed through carding and drafting, and then spun into a singles yarn. Two or more singles yarns are combined, typically by twisting them together, to form a plied spun yarn. In making a plied yarn from filament yarns two or more singles yarns are combined, typically by twisting them together, to form a plied yarn. The plied yarn (from filament or spun yarn) can be made directly by twisting the two singles yarns, with or without also twisting the individual singles yarn.
In either case, the plied yarns are subsequently treated with heat, called heatsetting, to set the twists permanently into the singles yarns. Heatsetting is considered an essential process in making conventional plied yarns. Without heatsetting, the plied yarns, upon being cut (such as in the manufacture of cut-pile carpet), lose ply-twist at the cut ends. The loss of ply-twist causes the singles yarns (or individual filaments if the yarn is a single ply) to separate from each other, considerably reducing wear performance. Furthermore, compressive forces, like that of foot traffic, will cause the individual filaments to flare and buckle, losing tuft resilience and giving the carpet a worn appearance.
Heatsetting is a labor, energy and capitol intensive process. Thus, heatsetting introduces expense into the manufacturing process. The heatsetting process involves unwinding the yarn to be heatset, heatsetting it and then rewinding it. Not only is it another processing step, but the generation of heat for the heatsetting step is expensive. Moreover, the equipment necessary to heatset requires capital investment. Heatsetting can also cause deleterious changes in the physical properties of yarn, such as shrinkage which may be non-uniform, luster, bulk, dyeability and other properties. It would be advantageous to eliminate the heatsetting step altogether and still obtain the benefits (e.g., locking of twist) achieved by it, without the disadvantages.
In the singles form, a conventional yarn that has been twisted, but not heatset, has torque and will form a tangled mass if tension on it is released, thus making it difficulty to process. It would be advantageous for some end uses to have a torque-free twisted singles yarn.